100w Solar Panel Wiring Question

[Pords]

Ive just ordered a 100w Panel with a 10 amp charge controller and remote meter. I’m happy with the way it all wires up part from the size of wire from controller to batteries. Been to Halfords and picked up 17amp wire to go from charge contorller to batteries. It does say on the back can be used for battery charging but no idea of wire gauge. Would this be sufficient? Max power outage from panel is 5.7 amps. Not blessed when it comes to understanding electrics.

Thanks

Jon

 

[RichardS]

17A wire should be fine for a 100W panel but it does depend upon how far the run is from the controller to the batteries. Obviously, the nearer the better but my controller warns against installing it in the same box as the batteries so it can be too near.

Richard

 

[Pords]

Thanks Richard
Batteries will only be 3-5 feet from controller so relatively short in length. Wiring direct from panel into controller and will be installing inline fuses of 10 amps.

 

[Norman_E]

It depends on the length of run (calculate as both wires, i.e a 5 metre run is 10 metres of wire) and on how much voltage drop you are prepared to accept. My own set up uses 4sq mm cross section wire for a 5 metre run. I don't know what 17amp wire is in terms of cross section because its a meaningless measure. Wire that will carry 12 volts at 17 amps with acceptable voltage drop over a metre or two would not do so over 20 metres.

I just saw your last post. The run from panel to controller has to be considered as well as that from controller to battery.

EDIT: I looked up so called 17 amp wire. Its about 2sq mm section, i.e. smaller than the 2.5mm wire I have seen recommended as the minimum for solar panels to connect with MC4 connectors.

 

[macd]

As Norman wrote.
It may be that 17A is the 'ampacity' of the wire, i.e. the maximum it can safely carry without exceeding the temperature rating of the insulation. For an acceptable voltage drop (bearing in mind you're going to a lot of bother to generate watts and won't want to waste them as heat) it's probably rather on the thin side. If you have a set of verniers you should be able to measure the diameter of the conductor, work out the x-sectional area, and then determine the voltage drop. Plenty of calculators on-line to do the latter, but do be sure they specify 'there and back' lengths of wire or not. Some are ambiguous.

 

[Pords]

In that case i will return back to Halfords and get something more appropriate in the region of 10 - 12 awg to be on the safe side. Panel to controller is about 15ft.

 

[macd]

Panel to controller is about 15ft.

...so you're looking at close to 40' of cable in total. Bear in mind that the run from controller to batteries will carry a max of around 8A.

 

[Pords]

Just had a look on the suppliers website and it states 2.5mm should be ok up to 100w and 8amps. Will pop in chandlers tomorrow and see what’s in stock.

 

[GrahamM376]

I was advised to use 6mm twin flex to avoid voltage drop. Why chandlers? Electrical suppliers such as City Elec. are usually far cheaper.

 

[lpdsn]

In that case i will return back to Halfords and get something more appropriate in the region of 10 - 12 awg to be on the safe side. Panel to controller is about 15ft.

Halfords is not going to be the cheapest place to go. Try looking online, something like 12V Planet.

As said above, there are two factors involved. One, will the current overheat the wire. Second what voltage will you lose.

The power generated is given by I^2 R. 2mm2 wiring shouldn't have difficulty with 10A.

For the second in practice it depends upon how flash your controller is. If it is just dropping the voltage (i.e. a basic one) losing a bit of voltage in the wiring will make no difference (within reason obviously - if you lose 12V in the wiring it will).

There are a number of calculators online of voltage drop for a given wire size and current.

Update: Just looked up a few figures. AWG14. 2mm2 wire has a resistance of about 8.3 Ohms/Km, or 0.083 Ohms per 10m length. So I^2 R at 10 A is 8.3W. Or 0.83W per metre. That's not going to boil the water for your tea.

Voltage drop at 10A will be 0.83V (two 5m lengths of cable). If you're just getting 20V at the panel it would mean 19.2V at the input to the controller. If that's just a straight drop to 14.4V then you'll lose nothing. If you've a flash MPPT controller you'll lose just over 4% of the power. The loss will be smaller at lower currents (i.e. lower sunlight levels etc.)

Further edit: although I've used 10A for some of the calcs above, that not going to come out of a 100W panel, which is much more likely to produce 5 ish A at nearly 20V. Anyway it gives an idea.

 

[whiteoaks7]

One thing people often overlook is that wiring exposed to sunlight (i.e. UV) will suffer insulation degradation - I bought some in a chandlers in Greece believing it would have UV filters in the insulation which car wiring would not have and a year later we could crumble the exposed insulation away. Now we have flexible conduit (which also crumbles) on the external wiring and we replace it regularly. Just a point to watch when you install your panel.

Otherwise, yes - buy big to reduce losses as everyone says.

Incidentally, you shouldn't assume you won't get 100W out of the panel (so about 8A) but that depends on where you sail.

 

[Norman_E]

In that case i will return back to Halfords and get something more appropriate in the region of 10 - 12 awg to be on the safe side. Panel to controller is about 15ft.

Forget Halfords and buy some proper marine grade tinned wire. For the length you have I would go for at least 4mm.

 

[aquaplane]

I mounted 100W on Seminole and had a 5-6 m run to the battery locker. As they were 2x50W panels I wired them in series to keep the volts up. I got a 15m 6mm solar panel cable off ebay

http://www.ebay.co.uk/itm/Solar-Pan...re-Crimped-TUV-double-insulated-/232478987279

which is good for outdoor use.

I cut it in half and used the MC4 connectors outside where they were in the weather. The Vitron MPPT controller drops the voltage for the last meter between the controller and the batteries. The low voltage high amp distance is minimised. It seems to work.

 

[Quandary]

Forget Halfords and buy some proper marine grade tinned wire. For the length you have I would go for at least 4mm.

He won't get it in Halfords anyway, unless things have changed recently they only stock that '17amp' wire in little spools, I have never noticed anything heavier in there. Plenty of 12v wiring supplies on line or at an auto electrician, though they are less likely to have the tinned stuff.

 

[Pords]

Thanks guys for all the advice which has been duly noted. Will sit down tomorrow and work out what I need and who to go to.

Regards

Jon

 

[William_H]

I think people get over obsessed with "voltage drop" in a battery charging line. Volt drop is a concern in things like mast head incandescent lamp where a resistance in the wire causes a volt drop which reduces current which reduces total watts.
However in a battery charging situation a volt drop in the wire reduces the voltage at the battery which reduces the current into the battery which there for reduces volt drop. So it is self adjusting and actual amps into the battery is only slightly reduced. Being even less significant as battery charge rises so current falls anyway.
I am not advocating light wire because light wire will be more susceptible to corrosion or other damage so heavy is more robsut but don'r worry quie so much about volt drop. olewill

 

[ghostlymoron]

"Halfords is not going to be the cheapest place to go. Try looking online, something like 12V Planet."
I've found Halfords useful when I've needed small quantities in a hurry in which case it's not worth shopping around. Otherwise go online. I only use tinned in exposed situations for cost reasons. Never been a problem.

 

[Graham_Wright]

I was advised to use 6mm twin flex to avoid voltage drop. Why chandlers? Electrical suppliers such as City Elec. are usually far cheaper.

Tinned or plated cable has benefits.

 

[Ian_Edwards]

I think you need to be very careful about the conductor size and loses through connectors, even a small resistive load can make big difference.

Loss in watts is calculated as; I^2 * R, i.e. the square of the current times the resistance, so if you have resistance of just 1 ohm on a 100 watt panel, which will have an output current of around 8 amps (depending on what kind of controller you use), the power loss in the cable will be 64 watts or 6.4% of the power generated by the panel.

If you get the resistance down to 0.1 ohms at 8 amps, then you lose just 6.4 watts or 0.64%, but 6.4 watts will power 2 typical LED cabin lights.

As an illustration I've produced a simple table to illustrate the power loss in the cable.

So the message is, use as large a cross section cable as is sensible and be very careful with connections, and be aware the at the sub 1 ohm level, most cheap multimeters won't be very accurate.

A well designed and built system should be able to get the two way resistance below the 0.1 ohm level, but even a slightly poor connection will significantly reduce the useful power output from a panel.

		resistance in ohms
		1	0.5	0.25	0.1
amps	amps^2	watts	watts	watts	watts
1	1	1.00	0.50	0.25	0.10
2	4	4.00	2.00	1.00	0.40
3	9	9.00	4.50	2.25	0.90
4	16	16.00	8.00	4.00	1.60
5	25	25.00	12.50	6.25	2.50
6	36	36.00	18.00	9.00	3.60
7	49	49.00	24.50	12.25	4.90
8	64	64.00	32.00	16.00	6.40
9	81	81.00	40.50	20.25	8.10
10	100	100.00	50.00	25.00	10.00
11	121	121.00	60.50	30.25	12.10
12	144	144.00	72.00	36.00	14.40
13	169	169.00	84.50	42.25	16.90
14	196	196.00	98.00	49.00	19.60
15	225	225.00	112.50	56.25	22.50
16	256	256.00	128.00	64.00	25.60

 

[gregcope]

I mounted 100W on Seminole and had a 5-6 m run to the battery locker. As they were 2x50W panels I wired them in series to keep the volts up. I got a 15m 6mm solar panel cable off ebay

http://www.ebay.co.uk/itm/Solar-Pan...re-Crimped-TUV-double-insulated-/232478987279

which is good for outdoor use.

I cut it in half and used the MC4 connectors outside where they were in the weather. The Vitron MPPT controller drops the voltage for the last meter between the controller and the batteries. The low voltage high amp distance is minimised. It seems to work.

In 6mm that stuff looks good.

I did a 100W panel and 2*50w panels all woth 6mm2 tinned wire off the internet.

Went for 6mm2 to reduce voltage drop, as you are going to great lengths generate power, you might as well maximise it. Youll want what that when trying to keepnup with a fridge...